1. Field of the Invention
This invention relates to the production of semiconductor devices by growing a native layer on silicon in a plasma.
2. Description of the Prior Art
In the production of semiconductor devices, including discrete devices and integrated circuits, one nearly universal step is the growth of an oxide layer on a silicon wafer. Typically, this is done on an undoped silicon wafer, or a wafer having a uniform doping level, as a prior step before subsequent selective doping operations. However, the growth of an oxide layer on silicon wafers having selectively doped regions may also be used. At the present time, the standard commercial method of oxidizing a silicon wafer, whether doped or undoped, is by heating the wafer in an oxygen atmosphere to a temperature on the order of 1100 degrees C. Occasionally, the oxidation is accomplished in a steam atmosphere. Small amounts of chlorine may be introduced in the oxidizing atmosphere to remove impurities, especially sodium, from the oxide layer. However, the elevated temperatures required for such thermal oxidation leads to a slight warpage of the silicon wafer. This can be detrimental to the production of semiconductor devices having fine line widths, as the warpage interferes with obtaining adequate resolution and alignment in subsequent lithography steps. In addition, in the case of silicon wafers that already have portions selectively doped prior to the oxidation step, the high temperatures required by oxidation cause the dopants to diffuse somewhat in the silicon wafer. This may interfere in the operation or design or semiconductor devices, particularly those having very small gate regions, as in high density MOS devices.
Recently, work has been directed towards the plasma oxidation of silicon wafers. This includes placing the wafer in an oxygen plasma, which may be either a DC plasma or an RF plasma. A DC bias field is typically applied to the wafer in order to direct electrons and ion species from the plasma towards the wafer, resulting in increased oxidation rates. The primary advantage envisioned thus far for plasma oxidation of silicon wafers is that the oxide may be formed at a much lower wafer temperature, typically on the order of 600 degrees C. See, for example, "Anodization of Silicon in RF Induced Oxygen Plasma," by H. Q. Vu et al. in the Digest of Technical Papers of the 11th Conference on Solid State Devices, Aug. 27-29, 1979, Tokyo, Japan. This reference states that the number of stacking faults in plasma-grown oxides is less than that for thermally grown oxides on silicon.
However, current plasma techniques require a relatively high power plasma generator. For production line use, it would very desirable to increase the oxide growth rate without proportionally increasing the power requirements of the plasma generator.